The researchers associated with Excerpt 13.14 [not
shown here] deserve enormous credit for having specific plans in mind when they
designed their study and when they analyzed their data. Their research question
guided their statistical analysis, and their analysis did not follow the conventional
rules for making statistical comparisons in a two way ANOVA. Far too many applied
researchers erroneously think that (1) F-tests for main and interaction effects
must be computed and (2) comparisons of cell means can be made only if the interaction
is significant. This is unfortunate for several reasons, the main one
being that planned comparisons of cell means can sometimes produce interesting
findings that remain undetected by the standard F-tests of
a two-way ANOVA.